When an oil or gas well is drilled it is common to insert a liner or casing into the well in order to support the walls as the depth of the well is increased. In order to access oil or gas containing formation outside the casing, the casing is commonly perforated by means of explosives. As the casing is made of a hardwearing material such as steel, when perforation takes place the steel casing is deliberately damaged to provide access from the wellbore through to the formation and as a result, sections of the casing will be left with exposed metal shards or burrs directed into the wellbore.
Insertion of any other tools into the wellbore with such exposed shards or burrs, means the tools are susceptible to damage due to collisions with or scraping against the burrs formed during perforation. In particular, delicate screens used for the filtering of fluids downhole can easily be ruptured on contact with the burrs. It would therefore be advantageous to find a method of removing these burrs to avoid damaging tools downhole. One way to remove burrs may be to use a burr mill attached to a drill string and by rotation of the drill string through the wellbore, burrs may be removed.
It is a desire to make any connection between the main body of the tool and any external components such as a stabiliser, centraliser, mill sleeve etc. as strong as possible, because very large forces act on the burr mill in use leading to possible detrimental effects on the stability of auxiliary externally mounted components. There may be junk and debris that creates very high forces on the tool during normal usage. The environment for the connector also puts restrictions upon the fixation of such an external component. Furthermore, space for the connector is limited.
An ordinary screw and bolt connector may not be able to withstand the axial or rotational forces acting on the tool. In addition, vibrations may assist in backing out bolts and unscrewing screws and threaded connectors, thereby loosening the tool components. The environment for these kinds of tools is not an environment suitable for screw connectors.
A further problem is that screws and bolts may some times be forgotten completely to be attached. If remembered, they may be incompletely or incorrectly assembled.
It is thus desired to have a system for fixing a sleeve that is not only as strong as possible but also as safe as possible and as easy to use as possible. Additionally, it is desirable to avoid cumbersome arrangements from a technical and/or economical point of view. The present invention is directed to overcoming one or more of the problems as set forth above.